VDM's update not updating data on S/4

"No fields have changed" because you edited an offline entity instance, that you've just built yourself.

To get your example working little adjustments have to made:

OutbDeliveryItem item =  OutbDeliveryItem.builder()
  .deliveryDocument("some key")
  .deliveryDocumentItem("some key")
  .build();

// The following method registers a change of the entity.
item.setActualDeliveryQuantity(BigDecimal.TEN);

// Then execute the actual update operation, which only uses the actually changed fields.
service
  .updateOutbDeliveryItem(item)
  .execute(someDestination);

If the service is complaining about missing ETag provided, either follow the example described further below using the get-by-key appraoch. Or you explicitly tell the request to ignore the version identifer:

service
  .updateOutbDeliveryItem(item)
  .ignoreVersionIdentifier()
  .execute(someDestination);

That's it!

Alternatively, in order to implement the complete OData update workflow, you need to first get the entity by using the get-by-key method as described below.

String deliveryDocument;
String deliveryDocumentItem;
HttpDestinationProperties someDestination;

// First get the item by key.
OutbDeliveryItem item = service
  .getOutbDeliveryItemByKey(deliveryDocument, deliveryDocumentItem)
  .execute(someDestination)

// The following method registers a change of the entity.
itme.actualDeliveryQuantity(BigDecimal.TEN);

// Then execute the actual update operation, which only uses the actually changed fields.
service.updateOutbDeliveryItem(item).execute(someDestination);

This way, the ETag will be set internally. The entity version identifier is a requirement for most S/4 OData services to enable update/delete operations.

Note: You are not limited to get-by-key. You can also use the get-all method with filters to resolve multiple entities, in preparation for further update changes.